Warming up is important to a good training session. The purpose it the warm up it to prepare the body for strenuous exercise. Warming up joints and tissue helps people move better.
A warm up should also reinforce movement patterns and give people a chance to develop flexibility.
Another crittical component to the warm up it practicing the movements that will be done in the WOD. Many times short sets and teaching progressions help further prepare the athlete for the workout.
The skills set component is also where sensible scaling on loading should take place. If someone come in really isn't comfortable with the weight, this is their opportunity to change weights to something more manageable.
Pre/Post - Many people come in early before training. This time should be used to foam roll and stretch. After the WOD, foam rolling and stretching are important to recovery.
Each time you lift, take a moment to check yourself. Start from base up. Foot position, spinal alignment, placement relative to the bar.
People often have limitations based on flexibility. Other people may not be strong enough to hold position. Scale and adjust load until you have the both.